Method and device for cooling a motor vehicle engine

ABSTRACT

A method for cooling a motor vehicle engine consists in regulating the volume and the flow rate of a coolant fluid in a hydraulic circuit provided with a branch equipped with an electronically controlled actuator and means forming radiator. The method comprises a step of determining the temperature of the cooling liquid, a step of comparing the temperature of the cooling liquid with a specified threshold temperature from which the engine is said to be hot, and, when the temperature of the fluid is higher than the threshold temperature, the flow rate in the radiator branch is regulated so as to maintain the temperature of the cooling fluid around a specified setpoint value. The curve representing the opening of the thermostat valve based on the temperature of the cooling fluid exhibits an hysteresis around the setpoint temperature. The invention also concerns a device for cooling a motor vehicle engine.

The invention concerns a method and a device for cooling a motor vehicleengine.

The invention concerns more particularly a cooling device comprising ahydraulic circuit of a cooling fluid, associated with a pump forcirculating the cooling fluid through the engine of the vehicle anddifferent branches of the circuit. Thermal equipment of the vehicle canbe disposed in the different branches of the circuit.

Cooling systems are designed to ensure the resistance of engines to thethermo-mechanical stresses resulting from combustion. In addition,complementary functions are implemented, beyond the main cooling of theengine, in order to improve the overall efficiency or to provide andguarantee benefits to vehicle users, such as, for example, the heatingof the passenger compartment.

The cooling systems are dimensioned using only operation points atmaximum speed and full charge of the engine, and are thusover-dimensioned in the majority of usage cases of the vehicles.

Thus, the operation parameters of the engine are not optimized, whichleads to a degradation of its performances, such as increasedconsumption, a high level of emission of pollutants, as well as areduction in the heating and acoustic comfort of the vehicle.

Document EP557113 describes an engine cooling system comprising acooling liquid loop connected to a radiator, and means for regulatingthe flow rate of the liquid in this loop. The means for regulating theflow rate are dependent on operation conditions of the vehicle, inparticular by means of sensors of the temperature of the liquid disposedin different locations in the loop. The flow rate of the cooling liquidin the radiator loop is controlled in particular in order to regulatethe temperatures of the liquid at the outlet and at the inlet of theengine around respective setpoint values.

However, this system has a complex structure and uses a large number ofmeasured state variables, without optimizing thermal exchanges with thecooling liquid.

A purpose of the present invention is to propose a method for cooling amotor vehicle engine, correcting all or a part of the disadvantages ofthe prior art mentioned above.

This purpose is achieved in that the method for cooling a motor vehicleengine consists in regulating the volume and the flow rate of a coolingliquid in a hydraulic circuit provided with a branch equipped with anelectronically controlled actuator and provided with means formingradiator, the method comprising a first step of determining thetemperature of the cooling fluid, a step of comparing this temperaturewith a specified threshold temperature from which the engine is said tobe “hot”, and, when the temperature of the fluid is higher than thethreshold temperature, the flow rate in the radiator branch is regulatedso as to maintain the temperature of the cooling liquid around aspecified setpoint value, characterized in that the curve representativeof the opening of the thermostatic valve in function of the temperatureof the cooling fluid exhibits an hysteresis around the setpoint value,so as to regulate the temperature of the cooling liquid at said setpointvalue.

Another purpose of the present invention is to propose a cooling devicefor a motor vehicle engine, correcting all or a part of thedisadvantages of the prior art mentioned above.

This purpose is achieved in that the cooling device for a motor vehicleengine is of the type comprising a hydraulic circuit of a cooling fluid,associated with a pump for circulating the fluid through the engine ofthe vehicle and different branches of the circuit, in which are arrangedthermal equipment of the vehicle, at least some of the branches of thecircuit being equipped with electronically controlled actuators toregulate the circulation of the fluid in these branches, the devicecomprising means for collecting information relating to the operationconditions of the vehicle, connected to means for controlling theoperation of the actuators, in order to regulate the volume and the flowrate of fluid circulating in the hydraulic circuit so as to optimize theoperation of the engine, the circuit comprising a branch equipped withan electronically controlled actuator and provided with means formingradiator, the means for collecting information being adapted todetermine the temperature of the cooling fluid, so that, when thetemperature of the fluid is higher than a specified threshold value fromwhich the engine is referred to as “hot”, the control means regulate theflow rate in the radiator branch so as to maintain the temperature ofthe cooling liquid around a specified setpoint value, characterized inthat the actuator of the radiator branch is constituted by athermostatic valve adapted to be electronically controlled, and in thatthe curve representative of the opening of the thermostatic valve as afunction of the temperature of the cooling fluid has hysteresis aroundthe setpoint temperature, so as to regulate the temperature of thecooling liquid at said setpoint temperature.

Further, the invention can comprise one or several of the followingcharacteristics:

-   -   the setpoint temperature is between 60 and 120 degrees        approximately,    -   the control means cooperate with the information collecting        means to determine the temperature of the intake air of the        engine, so as to increase the flow rate in said branch when the        temperature of the intake air of the engine increases beyond a        specified first threshold,    -   the control means increase the flow rate in the radiator branch        when the temperature of the intake air of the engine increases,        so as to ensure a maximum flow rate in the branch when the        temperature of the intake air of the engine reaches a specified        second threshold,    -   the control means cooperate with the information collecting        means, in order to determine the speed of the vehicle, so as to        increase the flow rate in said branch when the speed of the        vehicle increases beyond a specified first threshold,    -   the control means increase the flow rate in the radiator branch        when the speed of the vehicle increases, so as to ensure a        maximum flow rate in the branch when the speed of the vehicle        reaches a specified second threshold,    -   the device comprises ventilation means, or “Motor Ventilation        Group”, adapted to cooperate with the means forming radiator,        the control means ensuring the control of the ventilation means        as a function of the temperature of the cooling liquid, so that        the rotational speed of the ventilation means increases when the        temperature of the cooling fluid increases,    -   the increase in the rotational speed of the ventilation means is        controlled as a function of the speed of variation of the        temperature of the cooling liquid, the rotational speed of the        ventilation means as a function of the temperature of the        cooling liquid follows a line whose slope is proportional to the        speed of variation of the temperature of the cooling liquid,    -   the ventilation means are started when the temperature of the        cooling liquid is higher than the setpoint value and the flow        rate of the cooling liquid in the radiator branch is        substantially maximum,    -   the control means cooperate with the information collecting        means to determine the temperature of the air located under the        vehicle hood, so as to start the ventilation means when the        temperature of the air located under the hood is higher than a        specified threshold.

Other characteristics and advantages will appear in reading thefollowing description, made in reference to the drawings in which:

FIG. 1 shows schematically the structure and the operation of an exampleof embodiment of the cooling device according to the present invention,

FIG. 2 shows, on a same graph, an example of variation in the course oftime t of the temperature T of the cooling liquid and of a firstthreshold temperature T₁,

FIG. 3 shows the variation of a setpoint temperature Tc as a function ofthe torque C of the vehicle engine, the engine speed being constant,

FIG. 4 shows the variation of the percentage of opening of the radiatorvalve as a function of the temperature T of the cooling fluid,

FIG. 5 shows an example of variation of the electric pulse I to controlthe radiator valve as a function of the temperature of the intake air Taof the engine, torque, engine speed, and vehicle speed being constant,

FIG. 6 shows the opening state of a bypass valve as a function of thetemperature T of the cooling liquid,

FIG. 7 shows schematically an example of coupling of the opening of thebypass valve as a function of the opening of the radiator valve,

FIG. 8 shows two examples of variation of the rotational speed of amotor ventilation group as a function of the variation of thetemperature T of the cooling liquid.

FIG. 1 shows a preferred example of embodiment of a cooling deviceaccording to the invention. The cooling device comprises a hydrauliccircuit 2 containing a cooling fluid.

A hydraulic pump 3 is associated with the circuit 2 in order to ensurethe circulation of the fluid through the engine 1 and different branches4, 5, 6, 7, 8, 44 of the circuit 2. Preferably, the pump 3 is a pump ofthe mechanical type, however, the use of an electric pump can also beenvisioned.

The branches 4, 5, 6, 7, 8, 44 of the circuit 2 are supplied withcooling liquid from a box 122, or “Water Outlet Box” (WOB). The box 122,which is affixed to the engine 1, and preferably to the engine block 1,ensures the collection of the cooling liquid having circulated in theengine 1. The cooling liquid that has circulated in the branches isitself recovered by a water input collector 23 before its recirculationin the engine 1.

Advantageously, at least some of the branches 4, 5, 6, 7, 8, 44 of thecircuit 2 are equipped with respective electronically controlledactuators 14, 15, 16, 17, 18, 29 for regulating the circulation of thefluid in these branches. The electronically controlled actuators are,for example, solenoid valves. In addition, the device comprises means 22for collecting information relating to the operation conditions of thevehicle. The collection means 22 are connected to the means 19 forcontrolling the operation of at least one part of the actuators 14, 15,16, 17, 18, 29, in order to regulate the volume and the flow rate of thefluid circulating in the hydraulic circuit 2 so as to optimize theoperation of the engine.

The control means 19 or information processing unit can comprise anyappropriate computer 20 such as, for example, an “Intelligent CouplingBox” (ICB) of a known type. The computer 20 is associated with means 21for storing information comprising, for example, a programmable memoryand/or a read-only memory. The computer 20 is also connected to means 22for collecting information relating to the operation conditions of thevehicle, comprising, for example, various sensors or other computerssuch as an engine control computer.

Preferably, the information collection means 22 are adapted to determineat least one of the following parameters: the speed of the engine, thetorque of the engine, the speed of the vehicle, the temperature of theengine lubrication oil, the temperature of the cooling liquid of theengine, the temperature of the exhaust gases of the engine, thetemperature of the air outside the vehicle and the temperature insidethe passenger compartment. The various items of information relating tothe operation conditions of the vehicle are processed and analyzed bythe computer 20, in order to control the operation of the actuators 14,15, 16, 17, 18, 29, and possibly, the operation of the pump 3.

According to the invention, the flow rate or the volume of coolingliquid allowed or not allowed to circulate in the different branches 4,5, 6, 7, 8, 44 of the circuit 2 is a function of the heated state of theengine 1. For example, it is possible to define three states of theengine 1, a first state in which the engine is referred to as “cold”, asecond in which the engine 1 is referred to as “hot” and a third statereferred to as “intermediate” between the hot and cold states.

Preferably, the thermal state of the engine 1 is characterized as afunction of the temperature T of the cooling liquid, preferably at theoutlet of the engine 1. Thus, when the temperature of the cooling liquidis lower than a specified first threshold temperature T₁, the state ofthe engine 1 is referred to as cold. Similarly, when the temperature Tof the cooling liquid is higher than a specified second thresholdtemperature T₂, the state of the engine 1 is referred to as hot.Finally, when the temperature of the cooling liquid is between the firstthreshold temperature T₁ and the second threshold temperature T₂, thestate of the engine 1 is referred to as intermediate.

The first threshold temperature T₁, and/or the second thresholdtemperature T₂ can be fixed or variable values specified as a functionof the type of the engine 1. Preferably, the first threshold temperatureT₁, and/or the second threshold temperature T₂ are variables as afunction of the type of engine 1 and of at least one operation parameterof the engine 1. For example, the first threshold temperature T₁, and/orthe second threshold temperature T₂ are functions of the average powerPm supplied by the engine 1. In other words, the control means 19cooperate with the collection means 22 in order to calculate the averageinstantaneous power Pm supplied by the engine 1.

The control means 19 then calculate the first threshold temperature T₁,and/or the second threshold temperature T₂, as a function of the averageinstantaneous power Pm and of a specified modeling of the operation ofthe engine 1. The modeling of the engine defines the cold, hot andintermediate states (first threshold temperature T₁ and second thresholdtemperature T₂) as a function of the average power Pm supplied by theengine.

The instantaneous power P(t) in kilowatts (kW) supplied by the engine atthe time t is given by the following equation:${{P(t)} = \frac{2 \cdot \pi \cdot N \cdot C}{60 \times 1000}},$where N is the instantaneous speed of the engine in rpm, and C is theinstantaneous torque of the engine in N.m. The values of the speed N andthe torque C can be measured by the information collection means 22,i.e., by appropriate sensors. Traditionally, the speed N of the engineis between 0 and 6000 rpm approximately, while the torque C is between 0and 350 N.m approximately.

The control means 19 then calculate the power P(t) supplied by theengine at the time t and the average power Pm(t) supplied by the engineat the time t. The average power Pm(t) at time t can be calculated bythe following equation:${{{Pm}(t)} = \frac{{\left( {t - 1} \right) \times {{Pm}\left( {t - 1} \right)}} + {{Pm}(t)}}{t}},$where Pm(t−1) is the average power at the time (t−1). Of course, theaverage power can be calculated by any other equivalent formula, suchas:${{{Pm}(t)} = \frac{{c \cdot {{Pm}\left( {t - 1} \right)}} + {{kP}(t)}}{c + k}},$where Pm(t−1) is the average power at the time (t−1), P(t) is theinstantaneous power at the time t, and c and k are weightingcoefficients.

The computer 19 and/or the information storage means 21 can contain themodeling of the operation of the engine 1, defining its cold state, hotstate, and intermediate state (first threshold temperature T₁ and secondthreshold temperature T₂) as a function of the average power Pm. Inother words, for a given type of engine, correspondence tables arecreated empirically and/or by calculation, giving the thresholdtemperatures T₁ and T₂ as a function of the average power Pm of theengine 1. These tables or models, which are a function of the type ofengine, are, for example, polynomial functions. The first thresholdtemperature T₁ is thus, in general, a decreasing function of the averagepower.

The first threshold temperature T₁ can vary between 20 and 60 degreesapproximately, and preferably between 30 and 50 degrees. The secondthreshold temperature T₂ can itself vary between 60 and 100 degreesapproximately. However, the threshold temperature T₂ is generallysubstantially constant around the value of 80 degrees.

Thus, the control means 19 cooperate with the information collectionmeans 22 in order to compare the temperature T of the cooling liquidwith the two threshold temperatures T₁ and T₂.

For purposes of simplification, the value of the first thresholdtemperature T₁, can be fixed by the control means 19 as soon as themeasured temperature T of the cooling liquid reaches the first thresholdtemperature T₁. Thus, FIG. 3 illustrates, in a same graph, an example ofvariation in the course of the time t: of the temperature T of thecooling liquid, and of the first threshold temperature T₁(Pm) which is afunction of the average power. In determining these temperatures T andT₁(Pm), it is noted that, for a given average power, from the time whenthe temperature T of the fluid reaches the first threshold value T1,this first threshold temperature T₁, varies slightly around a constantT₁f.

Referring to FIG. 1, the circuit comprises a branch 4 equipped with anelectronically controlled actuator 14 and provided with means 9 formingradiator. The radiator means 9 can be coupled to a motor ventilationgroup 30, which can also be controlled by control means 19.

According to the invention, the information collecting means 22determine the temperature T of the cooling fluid, so that, when it ishigher than the second threshold temperature T₂, the control means 19regulate the flow rate in the radiator branch 4 so as to maintain thetemperature T of the cooling liquid around a specified setpoint valueTc.

The setpoint temperature Tc is the temperature of the cooling liquidthat ensures an optimal operation of the engine 1. This setpointtemperature Tc is defined, for example, by a modeling of the concernedengine. The setpoint temperature Tc is, for example, between 60 and 120degrees approximately, and preferably between 80 and 100 degreesapproximately.

Preferably, the control means 19 cooperate with the informationcollecting means 22 in order to determine the setpoint temperature Tc asa function of the speed N and/or of the torque C of the engine 1.

Preferably, the setpoint temperature Tc is decreasing when the torque Cof the engine 1 increases. Similarly, the setpoint temperature Tcdecreases when the speed N of the engine 1 increases.

FIG. 3 illustrates an example of a curve representative of the variationof the setpoint temperature Tc as a function of the torque C of theengine, the engine speed N being constant. The setpoint temperature Tcfollows substantially a portion of a curve of the type Tc=A1+(A2/C^(n)),where Tc is the setpoint temperature, A1 and A2 are constants, C is thetorque, and n is an integer superior or equal to one. More precisely,for a engine speed N in the maximum Nmax order, when the torque C isunder or equal to half the maximum torque, the setpoint temperature Tcis substantially equal to 100 degrees. Further, when the torque C goestoward the maximum torque, the setpoint temperature Tc goes toward 80degrees approximately.

Similarly, the curve representative of the variation of the setpointtemperature Tc as a function of the torque C, the engine speed N beingconstant, can have a general shape comparable to the curve of FIG. 3.

The actuator 14 of the radiator branch 4 can be constituted by athermostatic valve adapted to be electronically controlled.Traditionally, the valve 14 can contain a part adapted to dilate orretract, in order to regulate the degree of opening of the valve as afunction of its temperature. In addition, the part adapted to dilate canalso be heated electrically in order to control in real time the openingand the closing of the valve.

FIG. 4 shows two examples of variation of the percentage of opening %Oof the thermostatic valve 14 of the radiator as a function of thetemperature T of the cooling fluid.

More precisely, FIG. 4 illustrates two examples of regulation of thetemperature T of the cooling fluid around two distinct setpointtemperatures respectively Tc1, Tc2. Thus, the curve of opening O of thethermostatic valve 14 exhibits a first hysteresis h1 around the firstsetpoint temperature Tc1 and a second hysteresis h2 around the secondsetpoint temperature Tc2. The succession of the closing F1, progressiveopening F2, opening F3 and progressive closing F4 phases of the valve 14is symbolized by arrows.

The first setpoint temperature Tc1 can correspond, for example, to aphase of strong solicitation of the engine, whereas the second setpointtemperature Tc2, which is higher, can correspond to a lower solicitationof the engine.

Of course, the invention is not limited to the preferred embodimentdescribed above. Thus, the actuator 14 of the radiator branch 4 can beconstituted by an electronically controlled proportional valve.

In this case, when the temperature T of the cooling fluid is higher thanthe setpoint temperature Tc by a specified difference dT in the order,for example, of 3 degrees, the control means 19 can increase the openingof the proportional valve 14. Similarly, when the temperature T of thecooling fluid becomes lower than the setpoint temperature Tc by aspecified difference dT in the order, for example, of 3 degrees, thecontrol means 19 can reduce the opening of the proportional valve 14.

Advantageously, the control means 19 can cooperate with the informationcollecting means 22, in order to determine the temperature Ta of theintake air of the engine 1 and to increase the flow rate of the coolingfluid in the radiator branch 4 when the temperature Ta of the intake airof the engine 1 increases beyond a specified first threshold S1.

Further, the control means 19 can ensure a maximum flow rate in theradiator branch 4 when the temperature Ta of the intake air of theengine 1 reaches a specified second threshold S2. The first temperaturethreshold S1 and second temperature threshold S2 for the intake air canbe in the order of 40 and 60 degrees, respectively.

FIG. 5 shows an example of variation of the electric pulse or intensityI for controlling the radiator valve 14, as a function of thetemperature Ta of the intake air of the engine, the engine speed N,torque C, and vehicle speed being constant.

Referring to FIG. 5, 11 corresponds to the electric impulsion providedto the actuator 14 (proportional electrovalve or thermovalve) for agiven setpoint temperature Tc1. This electric pulse 11, which is between0 and 100% of the maximum pulse, defines a specified partial opening ofthe actuator 14. When the temperature Ta of the intake air goes towardthe first threshold S1, the electric pulse I provided to the actuator 14goes toward I1.

When the temperature Ta of the intake air goes toward the secondthreshold S2, the electric pulse I provided to the actuator 14 increasesand goes toward the maximum pulse (100%), i.e., toward a total openingof the valve 14. This means that, for a given increase in the setpointtemperature Tc defining a given flow rate in the radiator branch 4, theincrease in the intake temperature Ta can generate a flow rate increase,even when the setpoint temperature Tc does not vary.

Similarly, the control means 19 can cooperate with the informationcollecting means 22 in order to determine the speed of the vehicle, soas to increase the flow rate in that branch 4 when the speed of thevehicle increases beyond a specified first threshold.

Similarly, the control means 19 can ensure a maximum flow rate in theradiator branch 4 when the speed of the vehicle reaches a specifiedsecond threshold.

The curve of variation of the electric pulse or intensity I forcontrolling the radiator valve 14 as a function of the speed of thevehicle can have a general shape similar to the curve in FIG. 5.

The first and second vehicle speed thresholds can be in the order of,respectively, half the maximum legal speed and the maximum speed.

As illustrated in FIG. 1, the circuit 2 comprises another branch 5equipped with an electronically controlled actuator 15 and associatedwith means 10 forming direct return of fluid or bypass. The controlmeans 19 can regulate the circulation of the cooling fluid in the bypassbranch 5 as a function of the temperature T of this fluid. Inparticular, the quantity of fluid allowed to circulate in the bypassbranch 5 increases when the temperature of the fluid increases from thefirst threshold temperature T₁, toward the second threshold temperatureT₂. Preferably, the electronically controlled actuator 15 of the bypassbranch 5 is of the proportional type.

As shown in FIG. 6, when the temperature of the fluid T is lower thanthe first threshold temperature T₁, the control means 19 can limit thecirculation of the fluid in the bypass branch 5 to a specified leakagerate. In other words, the actuator 15 of the bypass branch 5 ispartially open Of. For example, the partial opening Of of the actuator15 can ensure a leakage rate in the bypass branch 5 of between {fraction(1/50)} and ⅕ approximately of the maximum flow of the branch 5.

When the temperature of the fluid is higher than the second thresholdtemperature T₂, the control means 19 command at least temporarily thetotal opening O of the bypass actuator 15 (FIG. 6). In addition, whenthe temperature of the fluid is between the first threshold temperatureT₁ and the second threshold temperature T₂, the degree of opening of theactuator 15 can be at least temporarily proportional to the temperatureT of the cooling fluid. More precisely, between T₁ and T₂, the openingof the actuator 15 of the bypass increases when the temperature T of thefluid increases, and decreases when the temperature T of the fluiddecreases. The variation of the opening of the actuator 15 can beproportional to the temperature T of the fluid.

Advantageously, the curve that is representative of the opening of theactuator 15 as a function of the temperature T of the fluid can exhibitan hysteresis H. In other words, the increase in the opening of theactuator 15 begins after the temperature of the liquid T exceeds thefirst reference temperature T₁, by a specified first value E. Similarly,the reduction in the opening of the actuator 15 begins after thetemperature T of the liquid becomes lower, by a specified first value E,than the second reference temperature T₂. In other words, openings andclosings of the actuator 15 are done in a manner offset relative to thethreshold temperatures T₁ and T₂. The values E of these offsets are, forexample, in the order of 5 degrees.

Advantageously, when the temperature T of the fluid is higher than thesecond threshold temperature T₂, the control means 19 can command theactuator 15 of the bypass branch 5 as a function of the opening andclosing of the actuator 14 of the radiator branch 4.

FIG. 7 illustrates the percentage of opening %O of the actuators 15, 14of the bypass branch 5 and radiator branch 4 as a function of thetemperature T of the cooling liquid. As shown in FIG. 7, the controlmeans 19 can close F the actuator 15 of the bypass branch 5 when theactuator 14 of the radiator branch 4 is opened O. Similarly, theactuator 15 of the bypass branch 5 is opened O when the actuator 14 ofthe radiator branch 4 is closed F. Preferably, the opening of theactuator 15 of the bypass branch 5 is inversely proportional to theopening of the actuator 14 of the radiator branch 4.

Further, the closings and openings of the actuator 15 of the bypassbranch 5 can be performed with a specified temperature offset R relativeto the openings and closings of the actuator 14 of the radiator branch4. The temperature offset R can be in the order of a several degrees,for example, five degrees.

As shown in FIG. 8, the control means 19 can control the ventilationmeans 30 as a function of the temperature of the cooling liquid. Moreprecisely, the rotational speed of the ventilation means 40 can increasewhen the temperature T of the cooling liquid increases.

Preferably, the rotational speed V of the ventilating means 30 increasesproportionally to the speed of variation of the temperature of thecooling liquid $\frac{\mathbb{d}T}{\mathbb{d}t}.$FIG. 8 shows two examples of lines d1 and d2 representing the rotationalspeed of the motor ventilation unit as a function of the temperature Tof the liquid. The two lines d1 and d2 have different slopes eachrepresenting a speed of variation $\frac{\mathbb{d}T}{\mathbb{d}t}$of the temperature T of the cooling liquid. The speed of variation$\frac{\mathbb{d}T}{\mathbb{d}t}$of the temperature T of the cooling liquid can be calculated by thecontrol means 19.

Preferably, the ventilation means 30 are started when the temperature Tof the cooling fluid is higher than the setpoint temperature Tc and theflow rate of the cooling liquid in the radiator branch is substantiallymaximum.

Similarly, the control means 19 can cooperate with the informationcollecting means 22 in order to determine the temperature of the airlocated under the vehicle hood, so as to start the ventilation means 40when the temperature of the air located under the hood is higher than aspecified threshold.

Advantageously, the information collecting means 22 can be adapted todetect a possible malfunction of at least one of the electronicallycontrolled actuators. In this manner, when at least one failure of anactuator is detected and regardless of the temperature of the fluid, thecontrol means 19 can ensure free circulation of the fluid in at leastsome of the branches, and preferably in all of the branches. In otherwords, when a malfunction of the system is detected, all of the valvesof circuit 2 are opened.

Thus, it is easy to understand that the cooling device according to theinvention, while having a simple structure, makes it possible to manageheat exchanges in real time and in an optimum manner.

Finally, though the invention has been described in connection withspecific embodiments, it comprises all technical equivalents of themeans described.

1. Method for cooling a motor vehicle engine, consisting in regulatingthe volume and the flow rate of a cooling fluid in a hydraulic circuitprovided with a branch equipped with an electronically controlledactuator and provided with means forming radiator, the methodcomprising: a first step of determining the temperature (T) of thecooling fluid, a step of comparing this temperature with a specifiedthreshold temperature (T₂) from which the engine is referred to as“hot”, and when the temperature (T) of the fluid is higher than thethreshold temperature (T₂), regulating the flow rate in the radiatorbranch so as to maintain the temperature (T) of the cooling liquidaround a specified setpoint value (Tc), wherein the curve representativeof the opening (O) of the thermostatic valve as a function of thetemperature (T) of the cooling fluid exhibits an hysteresis around thesetpoint temperature, so as to regulate the temperature (T) of thecooling fluid at said setpoint temperature.
 2. Device for cooling amotor vehicle engine, of the type comprising a hydraulic circuit of acooling fluid, associated with a pump for circulating this fluid throughthe engine of the vehicle and different branches of the circuit, inwhich are arranged thermal equipment of the vehicle, at least some ofthe branches of the circuit being equipped with electronicallycontrolled actuators to regulate the circulation of the fluid in thesebranches, the device comprising: means for collecting informationrelating to the operation conditions of the vehicle, connected to meansfor controlling the operation of the actuators, in order to regulate thevolume and the flow rate of fluid circulating in the hydraulic circuitso as to optimize the operation of the engine, the circuit comprising abranch equipped with an electronically controlled actuator and providedwith means forming radiator, the information collecting means beingadapted to determine the temperature (T) of the cooling fluid, so that,when the temperature (T) of the fluid is higher than a specifiedthreshold temperature (T₂) from which the engine is referred to as“hot”, the control means regulate the flow rate in the radiator branchso as to maintain the temperature (T) of the cooling liquid around aspecified setpoint value (Tc), wherein the actuator of the radiatorbranch is constituted by a thermostatic valve adapted to beelectronically controlled, and in that the curve representative of theopening (O) of the thermostatic valve as a function of the temperature(T) of the cooling fluid exhibits an hysteresis around the setpointtemperature, so as to regulate the temperature (T) of the cooling liquidat said setpoint temperature.
 3. Device according to claim 2, whereinthe setpoint temperature (Tc) is between 60 and 120 degrees C.approximately.
 4. Device according to claim 2, wherein the control meanscooperate with the information collecting means, in order to determinethe temperature (Ta) of the intake air of the engine, so as to increasethe flow rate in said radiator branch when the temperature (Ta) of theintake air of the engine increases beyond a specified first threshold(S1).
 5. Device according to claim 4, wherein the control means increasethe flow rate in the radiator branch when the temperature (Ta) of theintake air of the engine increases, so as to ensure a maximum flow ratein the radiator branch when the temperature (Ta) of the intake air ofthe engine reaches a specified second threshold (S2).
 6. Deviceaccording to claim 2, wherein the control means cooperate with theinformation collecting means, in order to determine the speed of thevehicle, so as to increase the flow rate in said radiator branch whenthe speed of the vehicle increases beyond a specified first threshold.7. Device according to claim 6, wherein the control means increase theflow rate in the radiator branch when the speed of the vehicleincreases, so as to ensure a maximum flow rate in the radiator branchwhen the speed of the vehicle reaches a specified second threshold. 8.Device according to claim 2, which comprises ventilation means adaptedto cooperate with the means forming radiator, the control means ensuringa control of the ventilation means as a function of the temperature (T)of the cooling liquid, so that the rotational speed (V) of theventilation means increases when the temperature (T) of the coolingfluid increases.
 9. Device according to claim 8, wherein the increase ofthe rotational speed (V) of the ventilation means is controlled as afunction of the speed of variation$\left( \frac{\mathbb{d}T}{\mathbb{d}t} \right)$ of the temperature (T)of the cooling liquid.
 10. Device according to claim 9, wherein therotational speed of the ventilation means as a function of thetemperature (T) of the cooling liquid follows a line whose slope isproportional to the speed of variation$\left( \frac{\mathbb{d}T}{\mathbb{d}t} \right)$ of the temperature T ofthe cooling liquid.
 11. Device according to claim 8, wherein theventilation means are started when the temperature (T) of the coolingfluid is higher than the setpoint temperature (Tc) and the flow rate ofthe cooling liquid in the radiator branch is substantially maximum. 12.Device according to claim 8, wherein the control means cooperate withthe information collecting means, in order to determine the temperatureof the air located under the vehicle hood, so as to start theventilation means when the temperature of the air located under the hoodis higher than a specified threshold.
 13. Device according to claim 3,wherein the control means cooperate with the information collectingmeans, in order to determine the temperature (Ta) of the intake air ofthe engine, so as to increase the flow rate in said radiator branch whenthe temperature (Ta) of the intake air of the engine increases beyond aspecified first threshold (S1).
 14. Device according to claim 13,wherein the control means increase the flow rate in the radiator branchwhen the temperature (Ta) of the intake air of the engine increases, soas to ensure a maximum flow rate in the radiator branch when thetemperature (Ta) of the intake air of the engine reaches a specifiedsecond threshold (S2).
 15. Device according to claim 3, wherein thecontrol means cooperate with the information collecting means, in orderto determine the speed of the vehicle, so as to increase the flow ratein said radiator branch when the speed of the vehicle increases beyond aspecified first threshold.
 16. Device according to claim 4, wherein thecontrol means cooperate with the information collecting means, in orderto determine the speed of the vehicle, so as to increase the flow ratein said radiator branch when the speed of the vehicle increases beyond aspecified first threshold.
 17. Device according to claim 5, wherein thecontrol means cooperate with the information collecting means, in orderto determine the speed of the vehicle, so as to increase the flow ratein said radiator branch when the speed of the vehicle increases beyond aspecified first threshold.
 18. Device according to claim 15, wherein thecontrol means increase the flow rate in the radiator branch when thespeed of the vehicle increases, so as to ensure a maximum flow rate inthe radiator branch when the speed of the vehicle reaches a specifiedsecond threshold.
 19. Device according to claim 16, wherein the controlmeans increase the flow rate in the radiator branch when the speed ofthe vehicle increases, so as to ensure a maximum flow rate in theradiator branch when the speed of the vehicle reaches a specified secondthreshold.
 20. Device according to claim 17, wherein the control meansincrease the flow rate in the radiator branch when the speed of thevehicle increases, so as to ensure a maximum flow rate in the radiatorbranch when the speed of the vehicle reaches a specified secondthreshold.
 21. Device according to claim 2, wherein the thresholdtemperature (T₂) is a function of the average power Pm supplied by theengine
 1. 22. Device according to claim 2, wherein the setpointtemperature (Tc) is a function of speed N and/or torque C of the engine.23. Device according to claim 2, Wherein, when the temperature of thecooling fluid is lower than the second threshold temperature (T₂), theopening of an actuator of a bypass branch is at least temporarilyproportional to the temperature T of the cooling fluid.
 24. Deviceaccording to claim 23, wherein, when the temperature of the coolingfluid is lower than a first threshold temperature (T₁), the opening ofthe actuator of the bypass branch is limited to a specified leakagerate.
 25. Device according to claim 2, wherein, when the temperature ofthe cooling fluid is higher than the second threshold temperature (T₂),an actuator of a bypass branch is totally opened at least temporarily.26. Device according to claim 2, wherein, when the temperature of thecooling fluid is higher than the second threshold temperature (T₂), theopening of an actuator of a bypass branch is controlled as a function ofthe opening of the actuator of the radiator branch.
 27. Device accordingto claim 26, wherein the opening of the actuator of the bypass branch isinversely proportional to the opening of the actuator of the radiatorbranch.
 28. Device according to claim 27, wherein the closings andopenings of the actuator of the bypass branch are performed with aspecified temperature offset (R) relative to the closings and openingsof the actuator of the radiator branch.
 29. Method according to claim 1,wherein the threshold temperature (T₂) is a function fothe average powerPm supplied by the engine
 1. 30. Method according to claim 1, whereinthe setpoint temperature (Tc) is a function of speed N and/or torque Cof the engine.
 31. Method according to claim 1, wherein, when thetemperature of the cooling fluid is lower than the second thresholdtemperature (T₂), the cooling fluid flow in a bypass branch is at leasttemporarily proportional to the temperature T of the cooling fluid. 32.Method according to claim 31, wherein, when the temperature of thecooling fluid is lower than a first threshold temperature (T₁), thecooling fluid flow in the bypass branch is limited to a specifiedleakage rate.
 33. Method according to claim 1, wherein, when thetemperature of the cooling fluid is higher than the second thresholdtemperature (T₂), the cooling fluid flow in a bypass branch is maximumat least temporarily.
 34. Method according to claim 1, wherein, when thetemperature of the cooling fluid is higher than the second thresholdtemperature (T₂), the cooling fluid flow in a bypass branch iscontrolled as a function of the cooling fluid flow in the radiatorbranch.
 35. Method according to claim 34, wherein the cooling fluid flowin the bypass branch is inversely proportional to the cooling fluid flowin the radiator branch.
 36. Method according to claim 34, whereinvariations in the cooling fluid flow in the bypass branch are performedwith a specified temperature offset (R) relative to the variations inthe cooling fluid flow in the radiator branch.